1. Field Of The Invention
This invention pertains to the field of gas separation and, more particularly, gas separation by the use of semi-permeable membranes. More specifically, the present invention relates to the separation of gaseous components which are frequently present in various gas stream mixtures found in the production and/or reaction of polycrystalline and/or epitaxial silicon metals.
2. Discussion Of Related Art
Polycrystalline and epitaxial silicon metals employed in semi conductor usage are typically produced by the reduction and decomposition of silicon tetrachloride, trichlorosilane, dichlorosilane and/or silane. These silicon containing gaseous compounds are typically mixed with large concentrations of hydrogen gas and reacted at activation temperatures sufficient to effect reduction and decomposition whereby to deposit silicon metal by such reaction on predetermined substrates.
Thus, for example, in the production of polycrystalline silicon by a process commonly referred to as the Siemens-type process, trichlorosilane is reacted with hydrogen to form polycrystalline silicon on a heated elongated starter rod positioned within a bell jar reactor, as described in U.S. Pat. No. 3,979,490. In an alternative process, as described in U.S. Pat. No. 4,150,168, silane is thermally pyrolyzed in such a bell-jar type reactor in the presence of hydrogen to form the polycrystalline silicon on the elongated starter rod.
Instead of a bell jar type reactor, a fluidized bed has also been utilized to form polycrystalline silicon on seed particles as discussed in U.S. Pat. Nos. 3,012,861 and 3,012,862.
Silane, which may be used as a precursor material for the formation of the polycrystalline silicon, may be prepared by disproportionation as disclosed in U.S. Pat. No. 3,968,199 or by reduction of metallurgical silicon as discussed in U.S. Pat. No. 4,676,967.
So too, in the preparation of silicone compounds, silicon metal is generally hydrochlorinated to an intermediary product stream comprising trichlorosilane and hydrogen from which intermediary stream the final silicone compounds are ultimately prepared.
In essentially all of these techniques, there are gaseous streams produced which contain gas mixtures of one or more gaseous silicon compounds, such as halogenated halosilanes, and the like, which are in admixture with hydrogen and hydracids such as hydrogen chloride, and the like. Such gas mixtures may be present in intermediary process streams, waste streams, by-product streams, or even product streams as well.
Frequently, it is desirable to be able to separate these gaseous silicon components from the hydrogen or gaseous hydracids for purposes of purification and/or recovery of these various components. Processes which are currently available for such separation are generally either economically undesirable or are not very effective in achieving the desired separation. Indeed, in a number of instances, such as in the thermal pyrolysis of silane to form polycrystalline silicon, the exhaust gas consisting of silane and hydrogen is simply flared rather than attempting to separate the silane from the hydrogen.
A need accordingly exists for providing a technique in which the components of such gaseous mixtures may economically and efficiently be separated.